A novel layer-by-layer CNT/PbO2 anode for high-efficiency removal of PCP-Na through combining adsorption/electrosorption and electrocatalysis

Electrochemical oxidation is an effective mean to degrade non-biodegradable organics from the contaminated waters. However, its current efficiency is very low for the low-concentration organic pollutants treatment. In this work, combining with the outstanding adsorption property of CNT and the effective electrocatalytic oxidation performance of beta-PbO2, we constructed novel layer-by-layer carbon nanotube/PbO2 anodes (CNT/PbO2-3, CNT/PbO2-4 and CNT/PbO2-5) with high adsorbability to enhance the electrochemical degradation efficiency of low-concentration sodium pentachlorophenate (PCP-Na). In electrochemical oxidation tests, the PCP-Na was rapidly enriched in the CNT/PbO2 film through adsorption/electrosorption and then efficiently degraded in site. The removal efficiency of low-concentration PCP-Na (5 mg/L) on CNT/PbO2-4 reached 73.8% after only 5 min of electrolysis, whereas that on pure PbO2 was only 9.9%. To further clarify the mechanism of improvement of PCP-Na removal on CNT/PbO2-4 anode, the generation capacity of center dot OH radicals, oxygen evolution overpotential, voltammetric charge quantity, interface resistance, and specific surface area of CNT/PbO2-4 anode were also assessed and compared with those of other three anodes. Results showed that, in addition to the synergistic effect of adsorption/electrosorption and electrocatalysis, the more active sites, smaller electron transfer resistance and higher direct oxidation capacity of CNT/PbO2-4 anode also contributed to improving degradation rate of PCP-Na on CNT/PbO2-4 anode. Additionally the electrochemical degradation pathway of PCP-Na was also proposed based on the gas chromatography-mass spectrometry analysis. Finally, CNT/PbO2-4 electrode exhibited longer accelerated lifetime of 116 h than pure PbO2 electrode (91 h). Thus, these findings provide a new anode to improve the removal of low-concentration organic pollutants through combining electrochemical oxidation and adsorption/electrosorption processes. (C) 2019 Elsevier Ltd. All rights reserved.